Concrete block producers can achieve required fire ratings by blending normal weight and lightweight concrete, The Concrete Producer magazine, by Don Talend, brand storytelling, content management, and content strategy expert. Construction industry

1. O
ffering customers light-
weight concrete mason-
ry units is becoming
less of a value-added
marketing strategy and
more of a necessity for producers. In
booming market segments such as
schools, designers often require mini-
mum 2-hour fire ratings, while ma-
sons want more productivity and less
physical strain.
Even though block producers have
blended normal-weight sand with
lightweight coarse aggregate for years,
many have assumed that they could
promote fire resistance only with
100% lightweight aggregate units. For
many producers, the costs of the light-
weight aggregate itself and of trans-
porting it have made production of
100% lightweight units unfeasible, ef-
fectively shutting them out of projects
in which specifiers want a fire rating or
contractors want lighter units.
In response, a couple of lightweight
aggregate suppliers are using testing to
prove that blended units meet fire-re-
sistance requirements, enabling ma-
sonry to earn a bigger piece of the con-
struction market.
Blending a better block
The new International Building
Code has adopted ACI 216.1/TMS
0216.1, “Standard Method for Deter-
mining Fire Resistance of Concrete
and Masonry Construction Assem-
blies.” It provides for blending aggre-
gate as long as the unit meets the fire
rating in actual testing or if it is cast
with a minimum equivalent thickness
for a blended unit, calculable using
weighted averages found in Table 3.1
of the standard.
To calculate the equivalent thickness
of a 50/50 blended pumice/natural
sand unit to achieve a 2-hour fire rat-
ing, for example, establish the dry-
rodded weight of the aggregates to ac-
curately calculate volumes. Then add
the weighted averages to get the re-
quired equivalent thickness (see exam-
ple at left).
Using this method, two lightweight
aggregate suppliers have achieved Un-
derwriters Laboratories certification—
required in many markets by archi-
tects specifying fire-resistant
masonry—for blended units.
Last year Witelite by Tarmac of
Chesapeake, Va., supplier of a propri-
etary brand of pumice imported from
Greece, had several units with various
aggregate-blend ratios and equivalent
thicknesses fire-tested per ASTM E-
New evidence of fire resistance
in blended CMUs
Recent research confirms that producers can blend lightweight and normal-weight aggregate in their block
mix designs and achieve required fire ratings
Testing proves blended block of all shapes and sizes meet fire ratings.
WitelitebyTarmac
Equivalent thickness of a
100% pumice unit: 3.2 inches
Equivalent thickness of a
100% sand unit: 4.2 inches
(3.2 ‫ן‬ 0.50) + (4.2 ‫ן‬ 0.50)
= 3.7 inches
per ACI 216.1/TMS 0216.1
Calculating
equivalent thickness
for blended block

2. 119 by UL (Table 1, page 26). The goal
was to validate the ACI 216.1/TMS
0216.1 calculation method of blending
aggregate, says Dave Miller, manager
of technical marketing.
Augusta Concrete Block of Ham-
burg, S.C., recently switched its light-
weight aggregate supply to the Tarmac
material, and the research enabled it to
hit the ground running with a new
fire-rated block, says Jim Farmer, pres-
ident. “We’ve campaigned architects
to specify UL fire-rated block,” he
says. “I have plenty of jobs that have
50,000, 100,000 fire-rated block, and
when you’re able to use blended units
and they’ve been approved, that’s a big
savings right there.”
Not far away, Big River Industries of
Alpharetta, Ga., a supplier of rotary-
kiln expanded clay, developed in the
early ’90s a proprietary mix design for
fire-rated lightweight block that uses a
70/30 blend. “Our goal was to enable
our customers to use our mix design
on a blended unit so they didn’t have
to go out and do a fire test every time
they wanted to make a blended unit,”
says Jeff Speck, vice president of engi-
neering.
For Big River Industries’ customers
to provide a UL certificate on a light-
weight-specified project, their block
had to use 100% lightweight aggregate,
undergo a fire test at UL, or, if a
blended mix, meet the equivalent-
thickness requirements of normal-
weight block per ACI
216.1/TMS0216.1. Choosing the sec-
ond option, Speck wanted the flexibili-
ty to design the mix with either natural
sand, crushed limestone, or crushed
granite along with the lightweight ag-
gregate. If a blended mix including
natural sand passed the test, any of the
fines would be acceptable.
“We ran our initial fire test (Table
2), and the natural-sand combination,
which was high in silica, had the
[smallest] safety margin,” Speck says.
“We fire-tested that 70/30 blend on an
8-8-16 that had a 3.8-inch equivalent
thickness, and the blend with lime-
stone and the blend with granite went
well beyond 2 hours, and the one with
natural sand went just beyond 2
hours.” Dan Quinn, vice president at
Atlanta-area producer RMC Allied
Ready Mix, adds that the mix “pro-
duces an 8-inch block that’s 23
pounds; our regular 8-inch block is 28
pounds.”
Allowing a wholesale switch
With the fire-resistance hurdle
cleared, Mundelein, Ill.-based North-
field Block, a leading Chicago-area
block producer, is launching a gradual,
wholesale switch from normal- and
medium-weight units to blended light-
weight ones using Witelite by Tar-
mac’s pumice aggregate. To quantify
to masons and architects the value-
added benefits of lightweight units,
Northfield Block sales representatives
are handing out a two-page flyer titled,
“Protecting the Future of Masonry:
Lightweight Masonry Units.” The flyer
lists increased productivity, lower
Unit
Size Pumice Sand Cement Equiv
lb/cy lb/cy lb/cy thickness
8x8x16 2,520 4,150 740 3.8 in.
Test
Target Max avg Actual avg Max single Actual
temp to pass temp/time pt to pass temp/time
2 hr ambient + 250° F amb. + 325° F
333° F 333° F 408° F 408° F
2 hr 7 min 2 hr 6 min
*Percentages by volume. Actual dry-rodded weights were 48% pumice, 52% sand.
Table 1. UL fire testing of a 50/50-blended
pumice/sand concrete block*
In spring 1998 Witelite by Tarmac had a UL fire test conducted on several concrete masonry units
with varying volumetric ratios of sand and its proprietary brand of imported pumice. All the units met
test targets, including a unit with the highest sand percentage (50/50), which met the 2-hour target.
Source:WitelitebyTarmac
Unit
Unit Size Equiv Aggregate* Cement/agg
thickness ratio*
8x8x16 3.8 in. 70% expanded clay, 1:9
30% natural sand
Test
Target Max avg Actual avg Max single Actual
temp to pass temp/time pt to pass temp/time
2 hr ambient + 250° F ambient + 325° F 2 hr 8 min
320° F 320° F 395° F 395° F
2 hr 8 min 2 hr 8 min
*Volumetric measurement, based on dry-rodded unit weights of material.
Table 2. UL fire testing of Big River
Industries’ blended concrete block
In 1991 Big River Industries, Alpharetta, Ga., conducted full-scale UL fire tests on blended concrete
masonry units using several different normal-weight aggregates. All the units, including one cast
with natural sand that had the highest silica content, met the 2-hour test target.
Source:BigRiverIndustriesInc.

3. workers’ compensation costs, shorter
construction time, safer scaffolding,
and easier cutting with its lightweight
units. For architects, the flyer empha-
sizes lightweight block’s thermal resis-
tance, strength, durability, fire ratings,
and contribution to lower construc-
tion costs.
“I think for our future as a company,
we need to look at new products, in-
cluding lightweight products, for our
whole industry,” says Jeff Hunt, sales
manager. “When we came up with a
mix design where we could take 10
pounds out of an 8-inch block and still
have the durability to meet ASTM C
90 and make it cost-effective for the
basic contractor, that became very ex-
citing to us. Our 12-inch block is 33
pounds—that’s less than an 8-inch
block that’s currently in the market-
place; we’re cutting 14 pounds out—
that’s exciting.” s
—DON TALEND
Reference
ACI/TMS Committee 216, “Standard
Method for Determining Fire Resis-
tance of Concrete and Masonry Con-
struction Assemblies,” ANSI/ACI
216.1-97, TMS0216.97, ACI Manual
of Concrete Practice, 1999, American
Concrete Institute, Farmington Hills,
Mich.
The proven fire resistance of blended block is enabling Northfield Block Co., Mundelein, Ill., and
managers (left to right) Jeff Hunt, Steve Hunt, Riley Fulmer, and Jenny Hunt to make a complete
switch to lightweight units.
Publication #J99L025
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